FIG. 1 schematically illustrates a configuration of a conventional bottom-gate TFT. The TFT comprises: a gate electrode 60, a gate insulating layer 70, a source electrode 20, a drain electrode 30, a semiconductor active layer 40 and a protection layer 90 formed on a base substrate 10. An array substrate comprising the TFT further comprises a passivation layer 50 and a pixel electrode 80. The gate electrode 60 of the bottom-gate TFT may block light from the backlight, preventing the semiconductor active layer 40 from being irradiated by the backlight and further causing the TFT to generate a leakage current. To prevent water and oxygen in the environment from affecting the semiconductor active layer 40, such configured TFT further has the protection layer 90 disposed above the semiconductor active layer 40. The protection layer 90 can prevent water and oxygen in the environment from affecting the metal oxide semiconductor active layer 40. However, the protection layer 90 in such a configuration is mostly a non-metal, which will cause the TFT to generate a leakage current. FIG. 2 schematically illustrates a configuration of a conventional top-gate TFT; the TFT comprises a drain electrode 200, a source electrode 300, an active layer 400, a gate insulating layer 500, a gate electrode 600 formed on a base substrate 100. An array substrate comprising the TFT further comprises a passivation layer 700 and a pixel electrode 800. In the top-gate TFT illustrated in FIG. 2, the gate electrode 600 can prevent the ambient light from affecting the semiconductor active layer 400. The drain electrode 200 and the source electrode 300 are separated from each other, light from the backlight can pass through the transparent base substrate 100 and irradiate the semiconductor active layer 400. Moreover, the semiconductor active layer 400 contacts the drain electrode 200 and the source electrode 300 at the same time. After being irradiated by the light, the semiconductor active layer 400 will generate a conductive passage between the drain electrode 200 and the source electrode 300, thereby causing the TFT to generate a leakage current.
It is seen from the above that the conventional top-gate TFT can easily generate a leakage current under the influence of the backlight.